The present invention is directed to an apparatus for precisely capturing measurements from remote and inaccessible locations and transferring that information in an enhanced and highly accurate representation to monitoring, recording and especially controlling devices which may be physically distant from the sensors.
The invention particularly applies to the measurement of moisture in the soil, in earthworks, in cement castings, and in other bulk materials, whether solid or fluid, of homogeneous or heterogeneous constitution, however varying in composition, shape, particle distribution, compaction, saturation, temperature, and chemical nature. Along with or alternate to the measurement of moisture, the invention may be applied to measuring temperature, pH, conductivity and other physical qualities of bulk media. The invention is particularly well suited to application where sensors and the sensor probe must function reliably and unattended for long periods of time. The sensor probe also incorporates refinements applicable to the gamut of practical measurement applications where accuracy, reliability, safety and flexibility of installation are important.
Control of irrigation systems is important for many reasons, especially to conserve resources such as water and fertilizer and to assure the optimal growth habit of irrigated vegetation.
The term "irrigation systems" as used here includes the entire range of horticultural applications from domestic lawn sprinklers to drip and mist systems to irrigation canals and moving structure sprinklers for agricultural production, plus other variants and applications not mentioned which will be readily evident to persons skilled in the art. Systems which deliver nutrients, pesticides, growth hormones and other stimulants, supplements, and inhibitors to plants are included in this scope of definition.
Among the many resources whose use may be optimized by improved control of irrigation systems are: water supplies, electrical energy for pumping and distributing water, fertilizing chemicals and management and cultivation labor.
Valuable qualities of agricultural, horticultural, and landscaping soils which may be preserved or conserved through skillful control of irrigation systems are soil aeration and consistency, naturally occurring mineral reserves, and embedded reserves of organic and inorganic amendments.
In addition to the cost of water itself, the use of water typically causes collateral costs of other valuable resources such as electricity for pumping and energy and materials for pre and post-use purification and transport.
Irrigation systems commonly in use today are subject to frequent and often incorrect manual adjustments to improve the results obtainable from timer-type open-loop controls. A special goal of this invention is to offer an alternative to this wasteful and sometimes counterproductive use of human labor by providing an effective and practical mechanism for using closed-loop control methods in the practice of irrigation.
An ideal irrigation process provides just the right amount of moisture to living plants under all variations of season, temperature, wind, topography, plant habit and other conditions affecting survival and growth of flora.
The invention which is subject of this disclosure materially advances the art with regard to the precision, convenience, and reliability of means for controlling the irrigation of living plants by measuring soil moisture and the related soil characteristics of pH, soluble mineral content, and soil temperature.
Irrigation systems and the plants they service may operate in an open loop or closed loop control process. In an open loop process, control actions are taken without respect to the actual conditions or circumstances of the controlled element. Clock timers which operate irrigation valves to water plants at preset fixed intervals are an example of an open loop process. These require continuous management and manual interaction to provide a suitable result without waste.
Because open loop processes are not responsive to the environment or even to the results-of their control actions, they are inherently unable to adapt to changing requirements except by the approximation of a fixed prearranged scenario of changes.
Open loop control processes are usually either off or on, since the lack of feedback information to regulate controls makes subtlety in output modulation largely irrelevant.
Where an open loop process is used to control a naturally changing phenomenon, such as the varying cycle of water demand experienced by growing plants as the seasons pass from Spring to Summer to Fall to Winter, the control process must, to avoid catastrophic failure in its mission, be set to allow for the "worst" or most extreme case which can be anticipated.
For irrigation systems this extreme case is the maximum water supply required to keep plants healthy on the hottest summer day in a blast of desiccating wind. On such a maximum day, if not provided with replenishing moisture, the plants may wither and die, drop fruit, or experience reduced vigor and yield.
One can readily see that on all days when actual water demand is less than the worst-case extreme one, a fixed program control which waters on the basis of worst case plant requirements will apply excess water.
The addition of a measurement method for soil moisture monitoring and its combination with a closed loop control process, as disclosed here, provides a greatly improved reliable means for effective feedback control of irrigation.